1. Field of the Invention
The present invention relates generally to a gland portion deformation preventing structure of a low pressure steam turbine and more particularly to a structure for preventing thermal deformation of the gland portion that is exposed to wet steam coming from an exhaust chamber.
2. Description of the Prior Art
FIG. 3 is a cross sectional view of a half portion of a double flow type low pressure steam turbine, which is known in the prior art. In FIG. 3, numeral 1 designates a rotor and numeral 2 designates a gland portion periphery of the rotor 1. Numeral 3 designates a gland casing, which surrounds the gland portion periphery 2 of the rotor 1. Within the gland casing 3, there is formed a passage (not shown) through which sealing steam for sealing the gland portion periphery 2 flows in or flows out. Numerals 4, 5 designate a seal portion, which comprises a labyrinth seal, etc. and is disposed so as to oppose the gland portion periphery 2. Thus, a gland portion is formed by the gland portion periphery 2 of the rotor 1, the gland casing 3 and the seal portion 4, 5.
Numeral 6 designates a casing, which forms therein an exhaust chamber 7. Numeral 8 designates a final stage stationary blade and numeral 9 designates a final stage moving blade. Numeral 10 designates a cavity, which is formed annularly between the exhaust chamber 7 and the rotor 1. Two apparatuses consisting each of the mentioned parts and components are disposed symmetrically in the right and left direction of the rotor 1 in the figure and steam 20 flows therein from the central portion to flow separately into steam paths of the right and left blade portions for rotation of the respective rotors 1.
That is, in the low pressure steam turbine constructed as mentioned above, the steam 20 of low pressure flows into the turbine portions from the central portion to flow through the steam paths wherein stationary blades and moving blades are disposed in multi-stages, including the final stage stationary blade 8 and the final stage moving blade 9. While the steam 20 so flows through the steam paths, it works to rotate the rotor 1 and then flow out into the exhaust chamber 7 and further into a condenser (not shown) to be condensed to water.
In the mentioned low pressure steam turbine, in order to seal an inside of the casing 6, where the steam flows, against an outside thereof in the gland portion periphery 2 of the rotor 1 at a downstream end portion of the casing 6, sealing steam is led into the gland casing 3 to maintain a predetermined pressure therein and then the sealing steam flows out into the cavity 10 via the seal portion 4, 5, as shown by the arrows which indicate the steam 22. Thereby the steam in the casing 6 is prevented from leaking outside along the gland portion periphery 2.
On the other hand, while the steam, which has passed through the final stage stationary blade 8 and moving blade 9 and finished its work, flows out into the exhaust chamber 7, a portion of the steam in the form of wet steam 21 may enter the cavity 10 through a gap 11 between the rotor 1 and a stationary portion of the exhaust chamber 7, etc. This wet steam 21, which has finished the work, is a low temperature steam having a high moisture content and cools portions of the seal portion 4, 5 and the gland casing 3 which are heated by the sealing steam in the vicinity of the gland portion in order to cause deformation of the gland casing 3, which, according to the extent of the deformation, causes the seal portion 4, 5 to come into excessive contact with the gland portion periphery 2 of the rotor 1 so as to generate vibration there.
As mentioned above, in the prior art gland portion of the low pressure steam turbine, the wet steam 21 that has finished the work may enter the gland portion via the cavity 10 and partially cool the gland casing 3 and the seal portion 4, 5 so as to cause the deformation of the gland portion, by which there arises the problem that the rotor 1 and the seal portion 4, 5 make excessive contact with each other, as the case may be, thereby generating vibration at this location.